Coralline algae take two different forms. Articulated species grow upright and have "branches" with flexible, uncalcified joints that withstand strong water motion. Crustose species encrust mostly on rocks, although they may also grow on plants or animals.
Like plants, however, the giant kelp harvests the sun’s energy through photosynthesis and does not feed on other organisms. This species is one of the fastest growing species in the world, and under perfect conditions, it has been known to grow up to two feet (60 cm) in a single day.
Phytoplankton, also known as microalgae, are similar to terrestrial plants in that they contain chlorophyll and require sunlight in order to live and grow. Most phytoplankton are buoyant and float in the upper part of the ocean, where sunlight penetrates the water.
Sargassum is a genus of large brown seaweed (a type of algae) that floats in island-like masses. Pelagic brown algae in the genus Sargassum. The berry-like structures are gas-filled bladders known as pneumatocysts, which provide buoyancy to the plant.